Light emitting diodes (LED) are, due to their relatively low energy consumption, long lifetime, and capability of electronic dimming, becoming more and more used in connection with lighting applications. LEDs are successfully used in lighting applications for general illumination such as, wash/flood lights illuminating a wide area or for generating wide light beams e.g. for the entertainment industry.
However, LEDs have not presently been successfully used in connection with light application systems where an image is created and projected towards a target surface. This is especially the case in connection with entertainment lightning, where a high demand for lumen output and high image quality are required. LED projecting systems have not yet been able to fulfill these requirements.
The light in projecting systems is generally collected into an optical gate where the image is generated, and an imaging optical system projects the gate onto a target surface. WO0198706, U.S. Pat. No. 6,227,669 and U.S. Pat. No. 6,402,347 disclose lighting systems comprising a number of LEDs arranged in a plane array where a converging lens is positioned in front of the LED in order to focus the light, for instance to illuminate a predetermined area/gate or for coupling the light from the diodes into an optical fiber.
U.S. Pat. No. 5,309,277, U.S. Pat. No. 6,227,669, WO0198706, JP2006269182 A2, EP1710493 A2, U.S. Pat. No. 6,443,594 disclose lighting systems where the light from a number of LEDs is directed towards a common focal point or focusing area, for instance by tilting the LEDs in relation to the optical axis (JP2006269182 A2, WO0198706, U.S. Pat. No. 5,309,277) or by using individually refracting means positioned in front of each LED (U.S. Pat. No. 6,443,594, U.S. Pat. No. 7,226,185B, EP1710493).
WO06023180 discloses a projecting system comprising a LED array with a multiple number of LEDs where the light from the LEDs is directed towards a target area. The LEDs may be mounted to a surface of a curved base as illustrated in FIG. 1a or to a surface of a plane base as illustrated in FIG. 1b. 
US 2008/0304536 discloses a high intensity lighting apparatus including an outer housing; a curved support disk having an array of diode or laser-based integrated light sources attached thereto disposed within the housing. Each of the light sources include a tube having a laser or diode chip at one end of the tube. The tubes each have at least one concave shaped exit surface on an end opposite the chip, wherein the concave exit surface converges light emitted from each of the light sources to focal points within the housing. A shape of the curved support disk converges the respective focal points into a light beam having a common focal plane. Adjustable secondary optics are disposed in the housing after the focal plane for creating various angles of transmission of the light beam. The laser can be a diode laser, while the diode can be a light-emitting diode (LED). The LED is encapsulated into the tube, where in one embodiment a tube has reflecting surfaces and a hybrid exiting surface. The hybrid exiting surface includes an inner spherical focusing element and outer parabolic focusing elements. Both the spherical 216 and parabolic focusing element 217 and 218 are configured to focus emitted light to the same focal point. The LED is encapsulated into the tube which optically reduces the efficient light emitting area of the LED and it is as a consequence difficult to maintain etendue through the entire optical system. Further it is difficult to design the focusing properties of the tube as focusing is performed by the hybrid exiting surface which constraints the designing options as only two surfaces parts can be adjusted. Yet another issue is the fact the high power LED used today often need cooling which is difficult provide when the LED is encapsulated into the tube.
US 2009/022552 discloses a light source-modulating device having composite curved surfaces comprises a light-distributing composite refractive surface, a base surface, a reflective surface and a light-modulating composite refractive surface, wherein the light-distributing composite refractive surface has a first and a second refractive surface, and the light-modulating composite refractive surface has a third and a fourth refractive surface. The light source-modulating device is particularly shaped so that light rays emitted from a light source and forming with a normal direction thereof an angle smaller than a light-distributing reference angle passes from the first refractive surface through the third refractive surface, which modulates an outgoing angle of said light rays; and light rays emitted from the light source and forming with the normal direction thereof an angle larger than the light-distributing reference angle passes from the second refractive surface to the reflective surface and is thereby reflected through the fourth refractive surface, which modulates an outgoing angle of said light rays. Thus, outgoing light rays emitted from the light source-modulating device are collimated and uniform.
U.S. Pat. No. 7,798,677 disclose an illumination unit for emitting light along an optic axis for a projection system includes an LED die and a collimator lens. The collimator lens includes a central part and a peripheral part. The central part has a first light transmission surface and a second light transmission surface opposite to the first light transmission surface. The peripheral part which is around the central part has an inner refraction wall coupled to the first light transmission surface to form a hollow for situating the LED die, an outer reflection wall opposite to the inner refraction wall, and a refraction surface connecting to the second light transmission surface and the outer reflection wall. The central part and the peripheral part of the collimator lens are oval and rotationally asymmetrical corresponding to the optic axis and both adapted to provide an elliptical light beam.
The prior art fixtures try to increase the lumen output by adding as many light sources as possible. The consequence is, however, that the efficiency with regard to power consumption versus light output is very low. Furthermore, a large amount of light is lost as the prior art fixtures typically only couple a central part of the light of the light beams through the gate in order to provide a uniform illumination of the gate, which again reduces the efficiency. The space in light fixtures is often limited and it is difficult to fit many light sources into prior art fixtures, for instance because the optical components associated with the light sources often take up a lot of space. Yet another aspect is the fact that color artifacts often appear in the output from fixtures having light sources of different colors. The reason for this is the fact that high performance LEDs used for stage-illumination have large, rectangular die areas of 5-12 mm2 and even higher This implies, that it is not possible to model the primary optics to a point source since the size-ratio between the primary optics and the LED die can get rather small. Furthermore, the rectangular shape can also be imaged in the output as rectangular patches. Compared to discharge lamps, these patches are ill fitted to smoothly fill out the circular spot profiles of stage-illumination instruments.